Some interesting points at the end of this article about how many comparisons of "housing affordability" are comparing apples and oranges. The main point is that housing affordability is not as good as people imply now because comparisons between 30-year fixed rates from today to the boom years doesn't reflect that much of the appreciation in the boom years was driven by adjustable and other exotic mortgage options that had lower initial costs than 30-year fixed rates.
http://www.zerohedge.com/news/2013-06-13/if-there-housing-recovery-then-chart-cant-be-right
These articles show the increase in ARM during the boom years.
http://www.newyorkfed.org/research/current_issues/ci16-8.pdf